Engine management system

ABSTRACT

A limited authority system for controlling engine performance in accordance with energy or thrust requirements in response to engine parameters which is capable of operating in a number of control modes.

This application is a continuation of application Ser. No. 358,931 filedMar. 4, 1982, abandoned.

This invention relates to fuel control systems and, more particularly,to an engine management system which may be coupled to a conventionalfuel control system for an aircraft to add limited authority controlwhich is capable, particularly on a multiple engine plane, ofeliminating a substantial amount of flight crew work necessary tooptimize thrust on takeoff and climb, synchronize engines at a desiredlevel of temperature, engine pressure ratio, engine speed or air speedduring climb or at cruise, and to provide fine tuning of engine controlsat flight idle configuration during descent. In addition, the system canbe used to optimize energy utilization through control of aircraftflight profile. As a result, significant fuel savings may be realized.

With respect to any vehicle engine, it is necessary to provide a fuelmetering device responsive to a suitable control for metering sufficientquantities of fuel to the engine to keep the engine running and toprovide motive power to the vehicle throughout its entire operatingrange. The control may be electronic, electro-mechanical, mechanical,hydraulic or of any other type suitable for responding to the inputsprovided thereto to command the desired response from the fuel meteringdevice.

The use of engines, and particularly gas turbine engines, in aircraftrequires particular care in fuel control to maintain its operatingrange, without inadvertently causing damage to the engines or otherwisecausing termination of operation of the engines. To this end, turbineengine fuel control systems have utilized numerous monitoring devicesfor sensing fan speed (N₁), gas generator speed (N₂) and turbine gastemperature (TGT) among other parameters and used this information tooptimize engine performance.

However, even with such complex fuel control circuitry, it is necessaryto closely monitor engine performance during the various flight modesand manually adjust the throttle levers for the engines so thatspecified engine conditions can be achieved during various operatingmodes of the aircraft.

During a typical flight, a substantial amount of throttle adjustmentmust be performed by the flight crew to obtain desired engine thrustlevels without exceeding safe engine operating limits. For example,during takeoff, the throttles will generally be set so that each engineachieves the maximum thrust configuration. During initial climb, theengines are preferably set to achieve maximum continuous thrust withoutexceeding the engine's maximum permissible limits, e.g. temperature orengine pressure ratio. During cruise operation, the engines may becontrolled to maintain precise temperatures or engine pressure ratios oraircraft cruising speeds while the engines are prevented from runningout of speed synchronization. During landing, the flight idle throttlelever positions must be continually monitored and adjusted to achievethe necessary thrust level as atmospheric conditions rapidly change uponreducing altitude.

Systems have been provided in the prior art which have monitored limitednumbers of engine or flight parameters to advise the crew of the correctthrottle settings or to provide one or more of the control functionsoutlined above, such as engine pressure ratio or air speed compensationof engines or synchronizing or synchrophasing of engines to theperformance of a designated master engine. Such prior art systemsgenerally operated to control engine performance in one of two ways. Onetype of system integrates the desired functions into a complex fuelcontrol computer, preferably of the electronic type. Another type ofcontrol device utilizes an autothrottle system.

Both approaches suffer substantial drawbacks. Autothrottle systems arevery expensive and carry substantial size and weight penaltiesassociated with the powerful drive motors required to maneuver thethrottle levers for fuel control. Additionally, automatic control withan autothrottle is difficult or impossible under conditions where thepilot maintains his hand upon the throttle levers for the purpose ofexercising additional manual control inasmuch as such manual controlactivates clutch devices which negate the effect of the autothrottle.Also, the great length of cable through which autothrottle commands mustbe sent to the fuel metering device can result in "hunting" by theautothrottle in seeking correct throttle settings. Complex computercontrol, while quite effective, generally requires the functions to bedesigned into the system at its inception rather than being laterintegrated into the computer system. As a result, retrofit of such asystem into an existing aircraft may be very difficult.

In accordance with this invention, an engine management system isprovided which monitors engine and external parameters to providelimited authority control of the engines throughout the variousoperating modes of an aircraft. In one aspect, engine characteristicssuch as shaft or spool speed, engine temperature or engine pressureratio may be controlled either for all engines or for a single masterengine with the remaining engines being synchronized to the selectedmaster. Alternatively, calibrated air speed or mach number can becontrolled with or without synchronization of the engines. In a secondaspect, flight characteristics of the airplane can be carefullymonitored and aircraft flight parameters, such as airspeed, climb rate,and altitude, can be controlled as well as engine parameters inaccordance with desired energy management characteristics, such thatdesirable flight characteristics, such as those yielding minimum fueluse, minimum flight time, minimum cost or maximum endurance can beobtained.

Authority over engine thrust is limited to a predetermined percentage ofthrottle travel and is established by interposing an adjustable memberin the trottle linkage in close proximity to the engine fuel meteringcontrol device. By such means, it is possible to retrofit substantiallyany aircraft even an aircraft already equipped with an autothrottle, toincorporate the engine management system of this invention. Further,drive motors of much lower weight and size than required forautothrottles may be utilized with a corresponding substantial reductionin system cost. In addition, throttle trim control may be achieved atall times by direct action on the engine fuel metering device controlwithout any motion of the throttle levers in the cockpit being producedthereby. Thus, grasping of the trottle levers by the pilot or locking ofthe throttle levers will not in any way impede the desired operation ofthe engine management system throughout the entire flight profile of anaircraft and no lag in response to system commands due to control cablelength will occur. If desired, electrical, mechanical or other suitablemeans may be provided to prevent modification of throttle settings bythe engine management system of this invention during certain modes offlight and in certain throttle lever positions.

The advantages of this invention will be readily apparent when thefollowing specification is read in conjunction with the appendeddrawings, wherein:

FIG. 1 is a schematic view of an aircraft which may be adapted with anengine management system in accordance with this invention;

FIG. 2 is a schematic representation showing engine control inaccordance with the prior art;

FIG. 3 is a schematic diagram similar to FIG. 2 illustrating enginecontrol showing the addition of an engine management system of thisinvention;

FIG. 4 is a cross-sectional view of an adjustable link for use in theengine management system of FIG. 3;

FIG. 5 is a schematic block diagram of an engine management computer anda control and display unit of the engine management system of of FIG. 3;

FIG. 6 is a schematic diagram showing electrical switching operation foruse in the engine management system of FIG. 3;

FIG. 7 illustrates the face of a control and display unit in accordancewith the preferred embodiment of this invention;

FIG. 8 illustrates a face of a control and display unit in accordancewith an alternate embodiment of this invention; and

FIG. 9 is an isometric view of a variable authority trim device for usein the energy management system of FIG. 3.

Referring now to the drawings, FIG. 1 illustrates an aircraft 10 havingengines 12 which are controlled by the flight crew through the use of athrottle quadrant 14 in the cockpit 16.

Referring now to FIG. 2, the throttle quadrant 14 is seen to contain aplurality of power levers or throttle levers 18, each of which isattached to move a drive lever 20. In the twin engine embodimentillustrated, the throttle quadrant will contain two power levers. Eachdrive lever 20 is connected through suitable means such as a cable 22 toa link 24 through which motion of the trottle lever 18 controlsoperation of a fuel meterin device 26 for providing operating fuel toits associated engine 12. While a straight link for conveying linearmotion is illustrated, rotary or other types of actuation may be usedand are adaptable to the engine management system of this invention.Each fuel metering device 26 will generally be a suitable fuel controlcomputer of an electrical, mechanical, hydraulic or other suitable typewhich acts in response to input from the throttle quadrant and frommonitoring devices responsive to engine and external parameters toprovide a precise control of its associated gas turbine engine.

In accordance with this invention, the engine control system is modified(see FIG. 3) by the installation of an engine management system 28 whichmonitors parameters of the engines 12 by way of suitable communicationsmeans such as conductors 30 and monitors external parameters by way ofconductor 32 for providing limited authority trim for the operation ofthe fuel metering devices 26.

Trimming operation is accomplished by the substitution of an adjustablelink 34 which has a variable dimension for modifying the effect on thefuel metering device 26 of changes in the position of the throttlelevers 18. The variable dimension link also permits limited adjustmentsof the fuel metering device 26 without any motion of the throttle levers18. Change in the variable dimension is provided by input to the link 34from the engine management system 28 through conductors 36.

The engine management system 28 may be contained in a single module ormultiple modules. In the preferred embodiment, a control and displayunit (CDU) 38 will be mounted in the cockpit and electrically connectedto an engine management computer (EMC) 40 mounted in a location remotefrom the cockpit which may be adjacent an engine nacelle or in theinstrumentation bay or at any other convenient location.

In the preferred embodiment, variable dimension link 34 (see FIG. 4) isin the form of an actuator of adjustable length. An outer tubular rod 42and an inner rod 44 are nested and provided with mating threads to serveas a jackscrew driven by an electric motor 46 through suitable gearing48. A first end 50 is preferably attached to cable 22 and a second end52 is attached to the fuel metering device 26 and is movable withrespect to the first end 50 upon threaded interaction of the rods 42 and44 to effect an expansion or shortening of link 34. Suitable bearings 54facilitate ease of rotation of the inner rod 44 while mechanical stops(not shown) may be used to insure prompt termination of rod rotation sothat the critical variable dimension of the link 34 will be preciselydetermined. Link 34 serves to convey motion of the throttle lever 18 tothe fuel metering device 16 and will be seen to modify the rate of uelflow provided at any given setting of the throttle lever 18 in responseto operation of motor 46. Except for changes in its variable dimensionproduced by operation of motor 46 in response to output of the enginemanagement computer 40, link 34 remains fixed in dimension and directlyconveys motion of the throttle lever 18 to the fuel metering device 26.

A centering switch 58 contains two sets of contacts which are operatedby actuators 60 and 62 when engaged by cam surfaces 64 and 66 of acentering switch cam 68 which is carried by the outer rod 42 for axialmotion of the link 34. When the variable dimension of the link is apredetermined length which is preferably midway between its fullyextended and fully shortened position, it is deemed to be centered andthe centering switch cam is situated such that both actuator 60 and 62are positioned in a depression 70 between cam surfaces 64 and 66 and notengaged thereby. Whenever the link 31 is extended or shortened from thiscentered position, either the actuator 60 or actuator 62 is engaged byits respective cam surface 64 or 66 so that the condition of the switchcontacts operated thereby is modified. Operation of the centering switchwill be further described subsequently herein.

FIG. 5 illustrates a basic block diagram of logic components of theengine management system 28. The control and display unit 38 which islocated in the aircraft cockpit accessible to the flight crew has adisplay section 72 for providing information to the flight crew of thefunctioning of the engine management system in addition to advising ofany possible malfunctions of the system or engine components detectablethereby. A microprocessor section 74 performs all memory and calculationfunctions required of the CDU 38. Input/output sections 76 permit directcontrol by the flight crew with respect to mode selection and the inputof controllable parameter values. Input/output sections of the CDU alsoprovide for communication between the control and display unit 38 andcorresponding input/output section 78 of the engine management computer40.

The engine management computer 40 also contains additional input/outputsection 80 which receives parametic inputs such as signals from theengines as well as other sources of information necessary for thecontrol of engine thrust or flight profile. Such parameters inputs mayinclude fan speed, gas generator speed, turbine gas temperature,altitude, total engine temperature, air speed, fuel use information,engine bleed status, and throttle lever or power lever angle. Thisinformation is fed to a microprocessor section 82 which, through the useof algorithms stored therein, calculates the approximate signal to betransmitted to the variable dimension links 34. At least one selectedengine performance characteristic such as those mentioned above iscompared with desired values for that engine performance characteristicrepresented by flight crew input of controllable parameter values. Thisinformation is also sent to the microprocessor section 74 of the controland display unit 38 wherein selected calculations are performed toverify these results. If the results of the calculations in bothmicroprocessor sections are consistent, the results are fed through theinput/output section 78 of the engine management computer 40 to controlthe electric motor 46 of the variable dimension line 34 (FIG. 4) so thatengine performance may be suitably controlled. If, however, the twomicroprocessor sections 74 and 82 calculate different engine trimsolutions, this is detected and annunciated by the system.

FIG. 6 illustrates switching functions which are performed within thepreferred embodiment of the engine management system of this invention.Electric motor 46 of the variable dimension link 34 comprises anarmature 84 and two field windings 86 and 88 which are wound so as to bein electrical opposition to each other such that energizing the motorthrough field winding 86 will cause rotation of the armature in onedirection and energizing the motor through field winding 88 and willcause rotation of the armature in the opposite direction. Thus, an opendriver 90 in the engine management computer 40 can be activated toprovide electrical power to field winding 86 and armature 84 through aconductor 92 to turn the armature in one direction to open or expand thevariable dimension link 34 while a close driver 94 can be activated toenergize field winding 88 and armature 84 through a conductor 96 toclose or shorten the variable dimension link 34.

Electrical power for the motor 46 is received from a voltage source 98which is connected by a conductor 100 through a normally open contact102a of a go around relay 102, a normally closed contact 104a of an airspeed relay 104, and a single pole, double throw throttle lever switch106. Throttle lever switch 106 has two positions. When the throttlelevers are set below flight idle position, the switch is in the positionillustrated in FIG. 6. At or above flight idle, the switch moves to thelower position. Power is also provided from the voltage source 98 to thecontrol and display unit 38 through a conductor 108 and to the enginemanagement computer 40 through a conductor 110.

The air speed 104 is energized by a signal transmitted either from theengine management computer 40 or directly from an air speed responsiveswitch (not shown) through a conductor 112 causing contact 104a to openwhen air speed reaches a predetermined value, preferably around 75knots. The go around relay 102 is energized by a signal from the controland display unit through a conductor 114 to hold contact 102a closedduring all phases of flight. This signal stops when the go around buttonis depressed to permit contact 102a to open. Conductor 114 alsotransmits this signal to a centering relay 116 operating a normallyclosed contact 116a and to primary relay 118 operating a single pole,double throw contact 118a. Contacts 116a and 118a are serially connectedto a voltage source 120 by a conductor 122 which terminates at centeringswitches 124 and 126 and contact 118a is connected to power lever switch106 by a conductor 127.

When energized through conductor 122, the centering switches, which areselectively actuated by either of actuators 60 or 62 being depressed byinteraction with the centering switch cam 68, act to bring the variabledimension link to its centered position. When the system is not in itsgo around mode, the centering switches 124, 126 will be energizedwhenever the throttle lever is at less than flight idle through acircuit comprising voltage source 98, conductor 100, contact 102a,contact 104a (or at above 75 kts, conductor 128 and contact 130a), powerlever switch 106, conductor 127, contact 118a, and conductor 122. Whenin the go around mode, the centering switches are energized by a circuitfrom voltage source 120 through contact 116a, contact 118a and conductor122. Whenever system power is turned off, the centering switches areenergized in the same manner as in the go around mode inasmuch asvoltage source 120 always remains energized.

A conductor 128 is connected to conductor 100 across the contact 104a ofthe air speed relay 104 and has a normally open contact 130a of atakeoff relay 130 interposed therein. The takeoff relay 130 receives anenergizing signal from the control and display unit 38 through aconductor 132 to short circuit the takeoff relay contact 104a in allmodes except the takeoff mode of the engine management system.

Operation of the engine management system of this invention will bedescribed in connection with a front panel 134 of the control anddisplay unit 38 illustrated in FIG. 7. While the front panel display andcontrols as shown in FIG. 7 are designed for use in a four engineairplane, it will be noted that the functions performed thereby aresuitable for use on any number of engines on a multiple engine plane.

A plurality of mode switches 136a-d may be selectively depressed todesignate an operating mode for the engine management system whichcorresponds to the flight mode of the aircraft. Mode switch 136a selectsthe takeoff (TO) mode. Mode switch 136b selects the maximum continuousthrust (MCT) mode. Mode switch 136c selects a turbine gas temperaturecontrol (TGT) mode. Mode switch 136d selects a flight idle (IDL) mode.While physically associated with mode switch 136a, indicator light 138,designated GA to identify the go around mode, is not a mode switch butmerely indicates when the go around mode has been selected by depressionof the go around switch (not shown) which is commonly found on theoutside of the throttle levers.

Synchronizing switches 140a-c are used to place the aircraft in a modewherein the engine management system serves to synchronize the engines.This may be accomplished in addition to or instead of selection of othermodes. Synchronizing switch 140a selects the synchronizing mode.Synchronizing switch 140b designates whether synchronization will bewith respect to fan speed (N₁) or gas generator speed (N₂).Synchronizing switch 140c controls the identity of the engine which willbe designated as master and with respect to which the other engines willbe synchronized.

A power switch (PWR) 142 controls the application of power to thedrivers which open and close the variable dimension links 34. Regardlessof the condition of power switch 142, power to the control and displayunit 38 and the engine management computer 40 is always maintained.Further, should the system be manually shutoff or become inoperative dueto power failure or other malfunction, the flight crew will stillmaintain full control of the fuel metering device through the link 34.Only the automatic trim operation provided by the engine managementsystem will be lost and regardless of system condition, full manualcontrol of the fuel metering device 26 will be maintained. When thepower switch is pressed to shut off the system, the link 34 is centeredin the manner previously described. Activation of test switch 144commences internal testing of the system.

Manual numerical inputs can be provided to the system through the thumbwheels on the front panel 134. Thumb wheels 146 permit setting of adesired turbine gas temperature to be utilized when the TGT mode isselected by depression of mode switch 136c. Operation of the referencetemperature thumb wheel 148 permits selection of a referencetemperature, generally provided by the control tower, for use by thesystem as a reference during takeoff.

Also provided are a digital display 150 for alternately displaying spoolspeed or engine temperature level and indicator lights 152a-d foradvising the flight crew of trim authority difficulties in connectionwith the aircraft propulsion engines.

With the power switch 142 in the "on" configuration, mode switch 136a isdepressed to place the engine management system in the takeoff mode. Inthis mode, the reference temperature thumb wheels 148 should be adjustedfor selection of the correct value of external ambient air temperaturefrom the tower (onboard sensors generally provide unreliable temperaturereadings when the aircraft is at rest on a hot runway) to provide a fullperformance takeoff. This temperature can be adjusted in a known mannerif a derated takeoff is desired.

Digital display 150 displays the takeoff N₁ target setting at which theengines are desired to run during takeoff, which is preselected inaccordance with the reference temperature, pressure altitude andaircraft and engine requirements. When the throttle levers 18 are in thetakeoff position, the engine management computer 40 will sense the fanspeed of each engine and send appropriate signals to the open driver 90or close driver 94 (FIG. 6) associated with the variable dimension link34 for each engine so as to maintain each engine's fan speed atprecisely the desired value by direct adjustment of the fuel meteringdevice 26 without any additional input from the flight crew and withoutmotion of the throttle levers 18.

If synchronizing switch 140a has been depressed before the throttlelevers are moved to takeoff position, the engine management system willoperate while the the throttle levers are being manually moved by thepilot to maintain the engines in synchronization as they are increasedin power. At about 95% of the target fan speed displayed on the digitaldisplay 150, synchronous operation will be terminated and each enginewill be brought independently to the target fan speed.

When the system is in the take off mode, takeoff relay contact 130a(FIG. 6) is open and go around relay contact 102a is closed. Thus, thedrivers 90 and 94 for motor 46 are energized to control trimmingoperation of the engines 12 as soon as the throttle levers have passedflight idle position at which point throttle lever switch 106 isswitched from the position illustrated in FIG. 6 to complete theenergization circuit and permit the links 34 to depart from the centeredposition.

As the plane is accelerating on its takeoff run, the engine managementsystem 28 continues to maintain all engines at the desired fan speed.However, at the preset air speed of around 75 kts., the air speed relay104 receives a signal to open contact 104a. This removes operating powerfrom the drivers 90 and 94 and thus terminates any further trimoperation by the system in the takeoff mode. However, no conductive pathfor energizing the centering switches 124 and 126 is completed and sothe links 34 remain at the position to which they were commanded beforeair speed relay contact 104a opened. This operation is provided tosatisfy requirements that no active automatic throttle control be inoperation at takeoff. After operation in the takeoff mode has terminatedby selection of an alternate mode, a signal is sent by CDU 38 to thetakeoff relay 130 to close contact 130a, thus bypassing air speed relaycontact 104a to resume trim operation of the engines 12 by the enginemanagement system 28 without regard to aircraft speed.

Depression of mode switch 136b places the system in the maximumcontinuous thrust mode. Upon selection of this mode, a turbine gastemperature target which is determined by the engine manufacturer andpreset into the system microprocessors is displayed on the digitaldisplay 150. Trim actuator links 34 are controlled to maintain theengines at this value of turbine gas temperature without surpassing N₁and N₂ overspeed limits. Preferably, no engine synchronization isprovided in this mode.

Near the end of aircraft climb or upon reaching cruising altitude, thepilot may press mode switch 136c for selection of the turbine gastemperature mode. When this mode is selected, the TGT value entered onthe thumb wheels 146 is displayed on the digital display 150. Allengines are then controlled through lengthening or shortening of theindividual engines' actuator links 34 to maintain this turbine gastemperature. If synchronizing switch 140a has also been depressed, onlythe master engine selected by synchronizing switch 140c will becontrolled at the desired turbine gas temperature and the remainingengines will be synchronized with respect to either N₁ or N₂ as selectedby synchronizing switch 140b in correspondence with that of the selectedmaster engine. It should be noted, however, that if any slave engineshould attempt to exceed its TGT limit to remain in speed synch with themaster engine, it will be constrained at the selected temperature andwill drop out of speed synch with the master engine.

When it is desired to land the airplane, mode switch 136d may bedepressed. When the throttle levers are placed in flight idle position,outside air temperature, altitude and bleed configuration of the enginesare provided to the engine management computer so that the proper valueof N₂ may be selected for the engines. The actual value of N₂ iscompared against the desired value and N₁ and TGT limit comparisons arealso performed to provide N₁ overspeed and TGT control protection. Asaircraft altitude decreases, the length of the variable dimension links34 are constantly adjusted to maintain proper flight idle levels priorto landing.

Should the pilot elect not to land the aircraft and depress the goaround button on the throttle levers, indicator light 138 will be lit toshow that the system has entered the go around mode. When this occurs,the signal from the control and display unit 38 (FIG. 6) throughconductor 114 is terminated, releasing the go around relay 102 to openswitch 102a removing power from the drivers 90 and 94 so that no furthercontrol of the links 34 will occur. Additionally, centering relay 116and primary relay 118 are released so that the switches 116a and 118areturn to the positions illustrated in FIG. 6. This connects voltagesource 120 through conductor 122 to the centering switches 124 and 126.Thus, if the link 34 (FIG. 4) is not in its centered position, such thateither actuator 60 (corresponding to centering switch 124) or actuator62 (corresponding to centering switch 126) is engaged by itscorresponding camming surface, winding 86 or 88, respectively, andarmature 84 will be energized and motor 46 will operate to return link34 to its centered position. When each link has been centered, thecentering switches will be opened and no further power will be receivedby the motors 46. Thus, upon entering go around mode, control is removedfrom the engine management system 28 and all of the variable dimensionlinks 34 are returned to their centered position.

Should the pilot elect instead to complete the landing, he will move thethrottle levers to below the flight idle position whereupon the throttlelever switch 106 will return to the position shown in FIG. 6. With goaround switch 102a closed, this will connect voltage source 98 to thecentering switches 124 and 126. Thus, when the throttles are moved tobelow flight idle position, power is removed from drivers 90 and 94 andthe variable dimension links 34 are brought to their centered position.

It should be noted that in the preferred embodiment the enginemanagement system is given limited trim authority over the fuel meteringdevice 26. Preferably, the full end to end stroke of the variabledimension link 34 will only be about 25% of the full authority fuelcontrol which may be accomplished by the throttle levers 18.

In case of malfunction of one or more engines, it is quite possible thatspool speed N₁ or N₂ or TGT temperature could vary from that of theremaining engines or exceeds its own limits by a sufficiently greatamount that it would be beyond the capacity of the engine managementsystem to correct. In this case, or whenever the throttles have exceededthe trim authority limit, indicator lights 152a-d advise the flight crewby lighting either the upwardly or downwardly directed arrow for theaffected engine to advise of the direction in which the thrust levermust be moved to bring the engine into an operational range where it canbe automatically trimmed in accordance with the requirements of thesystem.

FIG. 8 illustrates a front panel 156 for an alternate embodiment of acontrol and display unit 38A which shows one of many possiblemodifications in the operation of the engine management system of thisinvention wherein control is based on measurement of engine pressureratio and aircraft air speed. In this embodiment, which is shown by wayof example for use in a three engine aircraft, indicator lights 158perform, as before, the function of indicating when an engine requirestrimming beyond the capacity of the system which must then be performedby manipulation of the corresponding throttle lever. Mode switches160a-d are used to select the various flight modes while synchronizingswitches 162a and b control engine synchronizing operation. Power switch164, test switch 166 and reference temperature thumb wheels 168 are alsoprovided. Digital display 170 in this embodiment is used to displayengine pressure ratio. In addition, speed thumb wheels 172 are used toset a preselected value of mach number or calibrated air speed asselected by a speed selector switch 174.

When the takeoff mode is selected by depression of mode switch 160a andthe reference temperature obtained from the control tower has been setin reference temperature thumb wheels 168, the engine management systemwill control the engines to a computed engine pressure ratio which willbe displayed on the digital display 170. Additionally, if synchronizingswitch 162a has been depressed, synchronization of the engines will bemaintained as they are brought up to speed until they reach about 95percent of takeoff EPR.

When maximum continuous thrust mode is selected by depressing modeswitch 160b, synchronizing is preferably unavailable and the engines aremaintained at a preselected EPR value appropriate for climbingoperation.

Mode switch 160c selects cruise operation wherein the engines may bemaintained at an additional preselected EPR level. Synchronization isalso available on N₁ or N₂ and, as shown in this embodiment by way ofexample, it is not necessary to permit selection of a master engine. Thedesignated master may be preselected to always be the same or,alternatively, means may be contained in the microprocessor to measureselected engine parameters and perform computations to determine whichengine would best function as master for synchronizing purposes.

During cruise operation, it is also possible, by depressing mode switch160d, to select a constant air speed mode wherein the aircraft will bemaintained at the mach number or calibrated air air speed which has beenset into the speed thumb wheels 172.

In this embodiment, no provision is made for go around mode or flightidle mode. However, in these flight conditions, it may be desirable toprovide for an elimination of trim authority by mechanical means. Onesuch means is illustrated in FIG. 9 as an alternative form of variabledimension link 176.

Unlike link 34 illustrated in FIG. 4, link 176 is a rotary actuatorwhich affects trim operation along a circumferential dimension ratherthan a linear direction.

An input lever 178 is mounted for rotation on an axis 180 and has amounting post 182 adapted for connection to cable 22 (FIG. 3) so thataction of the throttle levers 18 can cause a resultant rotation of theinput lever 178 around the axis 180.

A connecting rod 184 has a first end mount 186 slidably mounted on posts188 of input lever 178 to permit radial motion of the connecting rod184. A second end mount 190 of connecting rod 184 rides in a slot 192 ofa trim link 194. A slot 196 of trim link 194 holds a trim rod 198, theposition of which is fixed as determined by operation of a trim motor200 which is electrically connected to the engine management computer40. A mounting post 202 of an output lever 204 has an end mount 206positioned in slot 192 axially spaced from the second end mount 190 ofconnecting rod 184. Output lever 204 is mounted for rotation about anaxis 208 which is preferably colinear with axis 180. An extended end ofmounting post 202a is adapted for securement to the aircraft fuelmetering device for controlling operation thereof. Connecting rod 184extends through a cam slot 210 of a cam 212 and has a cam follower 214adapted to move through the cam slot 210 engaging the camming surfacesthereof. In operation, action of the throttle levers is transmitted tothe input lever 178 which rotates about its axis 180 a shown by an arrow216. This rotation causes connecting rod 184 to similarly move resultingin rotation of trim link 194 around the fixed axis formed by the trimrod 198. Motion of the trim link 194 causes a corresponding rotationalmotion of the output lever 204 around its axis 208 such that the fuelmetering is adjusted by engagement with the mounting post 202. In thismanner, action from the throttle levers is directly passed to the fuelmetering device for control of fuel to the aircraft engines.

When the input lever 178 is in the position illustrated in FIG. 9, theaxes of the connecting rod 184 and mounting post 202 are laterallyspaced from each other within the slot 192. Thus, trimming operationsuch as previously described to be accomplished by the link 34 of FIG. 4can occur by energizing the motor 200 to cause motion of the trim rod198 in either direction designated by the arrow 218. This causes thetrim link 194 to rotate about an axis formed by the connecting rod 184which is more firmly positioned than the mounting post 202. Because ofthe distance between the axes of the connecting rod 184 and mountingpost 202, the mounting 202 is displaced circumferentially with respectto the input lever 178. As a result, fuel metering performance inresponse to positions of the aircraft throttle levers may be modified inthe same manner as was accomplished by the linear motion of link 34.

Link 176 permits a mechanical limitation of trim authority in accordancewith a preset schedule which forms the basis of design of the cam 212.As the throttle lever is moved in either direction such that the inputlever 178 moves to either end of its stroke, the cam follower 214 isurged radially outwardly by the cam surfaces of the cam 212. This causesthe first end mount 186 to move radially outwardly along the input lever178 while the second end mount 190 moves radially outwardly within theslot 192 of the trim link 194. This motion causes the axes of connectingrod 184 and mounting post 202 to come closer together. It will bereadily apparent that as these axes approach each other, motion of thetrim rod 198 and resulting rotation of the trim link 194 has a reducedeffect on motion of the output lever and, as the thrust levers are movedto their extreme positions, trim authority of the engine managementsystem is accordingly reduced. If desired, the cam can be designed sothat, at a desired point in the power lever stroke, the axes of theconnecting rod 184 and mounting post 202 coincide. In this position,regardless of the motion of the trim rod 198, no trimming action willresult from rotation of the trim link 194.

Thus an engine management system has been disclosed which may beinstalled in existing aircraft systems for providing limited authoritytrim operation of aircraft engine fuel metering devices such that finecontrol of engine thrust may be accomplished with a resultant saving infuel and in flight crew effort. Multiple mode operation can be providedthrough this system and, by selecting the engine and external parametersto be sensed, various bases of control can be provided. Additionally,mechanical limitation can be provided for the engine thrust trimoperation whereby, regardless of the amount of trimming called for bythe engine management system, he configuration of the link prevents anytrimming effect on the fuel metering device.

It should be noted that by the use of various algorithms for use by themicroprocessor in controlling flight profile, other means of control maybe effected. For example, the flight profile may be controlled formaximizing fuel conservation such that the minimum amount of fuel isused during the flight. Alternatively, a flight profile yielding minimumcost, whereby fuel usage is balanced against employee and equipment timeutilization in a prescribed manner, may be selected. If desired, aflight profile providing for the least time of flight or for arrival atspecified time could be selected. Further, it is possible to connect theengine management system of this invention to a flight navigationmanagement system such that altitude and course may be integrated forconsideration in the algorithm to be calculated whereby these factorscan be precisely controlled for optimizing flight characteristics.

I claim:
 1. An engine management system for an aircraft having at leastone engine, said engine management system having a plurality ofoperating modes corresponding to a plurality of flight modes of saidaircraft, said engine management system comprising:throttle meansincluding throttle lever means movable over a range of positions forcommanding corresponding rates of fuel flow to said engine; fuelmetering means operably connected to said throttle lever means andresponsive thereto for providing said corresponding rates of fuel flowto said engine; link means having a variable dimension adjustable over apredetermined range, said link means being operably interposed betweensaid throttle means and said fuel metering means for selectivelymodifying the rate of fuel flow provided by said fuel metering means inresponse to a position of said throttle lever means, the rate of fuelflow provided by said fuel metering means corresponding to the rate offuel flow commanded by said throttle lever means whenever said linkmeans dimension is of a preset value in said predetermined range; meansfor receiving parametric inputs representing desired engine performancecharacteristics, said parametric inputs including at least one of enginespeed and engine turbine temperature; means for selecting an operatingmode for said engine management system corresponding to one of saidflight modes of said aircraft, one of said operating modes being a goaround mode; link control means drivingly connected to said link meansfor controllably regulating said link means dimension and therebyselectively modifying said rate of fuel flow; means for energizing saidlink control means to modify said rate of fuel flow to the extentnecessary to achieve at least one of said desired engine performancecharacteristics, said energizing means energizing said link controlmeans and thereby modifying said rate of fuel flow in response to saidparametric inputs, said actual engine and aircraft performancecharacteristics, and said selected operating mode, said energizing meanscausing said link control means to bring said link means to said presetvalue whenever said engine management system is placed in said go aroundmode.
 2. An engine control system as in claim 1 wherein said link meansis mounted proximate to said fuel metering means.
 3. An enginemanagement system as in claim 1 wherein said link dimension is linear.4. An engine management system as in claim 1 wherein said link dimensionis nonlinear.
 5. An engine management system as in claim 1 wherein thepredetermined range of said link means dimension is not greater thanabout 25% of said throttle lever means range of positions.
 6. An enginemanagement system as in claim 1 wherein said preset value is generallyat the midpoint of said predetermined range.
 7. An engine managementsystem as in claim 1 wherein said link means comprises:a first memberhaving an end portion spatially fixed with respect to said throttlelever means; a second member having an end portion spatially fixed withrespect to said fuel metering means; means securing said first andsecond members for conveying motion from said throttle lever means tosaid fuel metering means; and drive means for selectively modifying thespatial relationship of said first and second member end portions.
 8. Anengine managment system as in claim 7 wherein said first member and saidsecond member are threaded for securement in jackscrew means forconveying motion of said throttle lever means to said fuel meteringmeans.
 9. An engine management system as in claim 7 wherein said firstand second members are mounted for rotation about an axis and said drivemeans is connected for changing the relative circumferential orientationof said first and second members.
 10. An engine management system as inclaim 7 including:a source of motive power; first centering switchingmeans operable to connect said drive means to said power source to causesaid link means dimension to be generally equal to said preset value;second centering switch means operably connected between said firstcentering switch means and said drive means for permitting applicationof motive power from said source to said drive means for shortening saidlink means if said link means dimension is greater than said presetvalue; third centering switch means operably connected between saidfirst centering switch means and said drive means for permittingapplication of motive power from said source to said drive means forlengthening said link means if said link means dimension is less thansaid preset value; and means for causing both said second centeringswitch means and said third centering switch means to preventapplication of motive power to said drive means when said link meansdimension is generally equal to said preset value.
 11. An enginemanagement system as in claim 1 wherein said aircraft has a plurality ofengines, each engine having a throttle lever means and fuel meteringmeans associated therewith and wherein said system includes a pluralityof said link means, each operably interposed between a throttle levermeans and its respective fuel metering device, and said link controlmeans is connected to each of said link means for individual controlthereof.
 12. An engine management system as in claim 1 wherein saidinput responsive means includes means for controlling enginetemperature.
 13. An engine management system as in claim 1 wherein saidinput responsive means includes means for controlling engine speed. 14.An engine management system as in claim 1 wherein said input responsivemeans includes means for controlling engine pressure ratio.
 15. Anengine management system as in claim 1 wherein said input responsivemeans includes means for controlling engine synchronization.
 16. Anengine management system as in claim 1 wherein said input responsivemeans includes means for controlling air speed.
 17. An engine managementsystem as claim 1 including modes corresponding to takeoff, climb andcruise.
 18. An engine management system as in claim 1 wherein thepredetermined range of said link means dimension is not greater thanabout 50% of said throttle lever means range of positions.
 19. An enginemanagement system as in claim 1 wherein one of said operating modes is atakeoff mode, said energizing means being inhibited from causing saidlink control means to modify said link means when said engine managementsystem is in said takeoff mode and air speed is above approximately 75knots.
 20. An engine management system as in claim 1, wherein saidenergizing means causes said link control means to bring said link meansto said preset value whenever said throttle lever means is below flightidle position.